Method for making odor sorbing packaging material

ABSTRACT

An odor sorbing packaging material is prepared by applying to at least one surface of a flexible substrate an odor absorbing coating containing an effective concentration of activated carbon. The packaging material may be converted into packages, bags, pouches, liner members, wrappers or the like for packaging products and other materials that generate objectionable odors.

BACKGROUND OF INVENTION

[0001] The present invention relates generally to a novel odor sorbingpackaging material and more particularly to a method for preparing sucha material that can be converted into packages for products whichgenerate objectionable odors.

[0002] One of the most widely accepted materials used to absorb odors isactivated carbon. Activated carbon is used in paperboard packaging,filters, gas masks and other devices to absorb and trap objectionableodors, aromas and other impurities. For example U.S. Pat. Nos. 5,540,916and 5,693,385, owned by the present assignee herein, disclose an odorsorbing packaging material comprising paperboard onto which there isapplied a coating comprising activated carbon. Other prior art whichdiscloses paper-based packaging containing activated carbon includesU.S. Pat. Nos. 2,593,146 which discloses laminated sheets for wrappingfoodstuffs, and U.S. Pat. No. 3,149,023 which discloses treatedpaperboard for packaging. U.S. Pat. No. 4,504,290 discloses a filterelement which contains activated carbon for odor control; U.S. Pat. No.4,517,308 discloses the use of activated carbon in filter mats, airfresheners, inner soles for shoes etc.; U.S. Pat. No. 5,022,553discloses a diaper storage container having a substantially rigid innerliner containing activated carbon; and, U.S. Pat. No. 5,860,391discloses the use of activated carbon in animal litter. However, as willbe noted, in each of the prior art teachings, the activated carbonapplications have been made primarily to rigid or semi-rigid products.Accordingly, it is an object of the present invention to incorporateactivated carbon into a non-rigid structure in an expeditious,economical and effective manner.

SUMMARY OF INVENTION

[0003] The present invention relates generally to packaging materialsand more specifically to a substantially flexible packaging materialthat has been treated to absorb the odors and aromas given off byproducts contained within packages constructed from the packagingmaterial. For this purpose, the present invention employs activatedcarbon, a material well known for its ability to absorb objectionableodors. In a preferred embodiment, the activated carbon is applied to oneor both surfaces of a flexible, polymeric film material usingconventional technology. However it is contemplated that other flexiblesubstrates such as paper onto which there is applied a polymer coating,or laminates of paper and polymer films could be used.

[0004] Activated carbon materials such as the NUCHAR products sold byWestvaco Corporation (the assignee herein), are available in particlesizes, or can be ground to particle sizes, which are readily dispersablein coatings, inks or the like suitable for application to flexible filmmaterials such as polyolefins. After application of the activated carbonto the film materials, the treated film can be converted into packages,liner elements, trash bags, pouches, wrappers or the like suitable foruse in many different applications where odor absorption is desired.

[0005] It is therefore, an object of the present invention to provide animproved method for applying an odor sorbing coating to packagingmaterial.

[0006] It is another object of the invention to provide an odor sorbingpackaging material with a sufficient concentration of activated carbonto accomplish the purpose of deodorizing substantially the entirety ofpackages converted from the packaging material.

[0007] And, finally, it is an object of the invention to provide ansubstantially flexible odor sorbing packaging material that may beconverted into various packages useful for a variety of purposes whichrequire odor control.

[0008] To satisfy these and other objects of the present inventioncontemplates the use of activated carbon dispersed in a binder that canbe applied to a polymeric film. Sub-micron carbon black is known for useas a coloring pigment in the manufacture of polyethylene resins toproduce black trash bags. However, attempts to use typical odor sorbingactivated carbons of larger particle size (5-40 microns) have beenunsuccessful because the presence of the particles have produced filmswith holes (voids) at higher carbon concentrations, or low odor sorbingcapacity at low carbon concentration. Likewise, attempts to apply anaqueous coating containing activated carbon to a polyolefin film havebeen less than successful. Such attempts have produced, on the one hand,coatings with a low carbon content (less than about 60%), that adheredwell, but performed poorly in odor tests, or coatings with a carboncontent greater than about 80%, with good odor sorption characteristics,but poor adhesion and excessive carbon rub-off. To overcome theseproblems, the present invention was developed. The present inventionsolves the problems referred to hereinbefore by applying the activatedcarbon containing coating in two steps.

DETAILED DESCRIPTION

[0009] The present invention is directed to the use of activated carbonin the manufacture of an odor absorbing packaging material. In thepreferred embodiment, the packaging material comprises a substantiallyflexible polymer substrate onto which there is applied a coatingcontaining activated carbon.

[0010] In one form of the present invention the substrate comprises alow density polyethylene (LDPE) film upon which activated carbon in anaqueous coating composition containing a suitable binder that adhereswell to LDPE is applied by conventional techniques such as coating,printing or the like. While LDPE is disclosed herein as a preferredsubstrate, other polymer films could readily be substituted with asuitable binder material. Examples of such polymer films arepoly-propylene, polyester, and polyamide.

[0011] An example of a suitable binder material for the preferred LDPEsubstrate is an aqueous styrene acrylate emulsion (identified as JONREZE-2064 from Westvaco Corporation's Chemical Division), that wets out theLDPE film to provide acceptable adhesion. “Wets out” in this contextmeans that the emulsion spreads easily on the film surface withoutbeading up. An aqueous binder system is preferred for the presentinvention as opposed to a solvent based system for environmental reasonsand because solvent recovery systems are complex and costly.

[0012] Initial coatings with up to 50% by weight of activated carbonhaving a particle size of about 5 microns adhered easily to LDPE filmwithout appreciable rub off, but performed poorly in odor absorptiontests. With 60% or more by weight activated carbon applied, significantrub off occurred and the products were deemed unacceptable. In order toincrease the concentration of carbon on the surface and reduce rub off,a two step process for applying the coatings was adopted.

[0013] The two step procedure involves an initial application of aprimer coating that may contain from about 0-50% by weight activatedcarbon, followed by a second coating application comprising acarbon/binder mixture of up to about 95% by weight activated carbon andthe remainder binder. The second application comprising up to 95% carbonadheres well to the first primer layer with no appreciable rub off andachieves a high concentration of activated carbon on the film surface toachieve good odor control.

[0014] Odor panel testing of samples prepared according to the inventiondemonstrated the effectiveness of the two step process. The results ofthe tests are shown in Table I. TABLE I Odor Panel Testing Carbon Sample1 hour 24 hours Odor (onion) 5 5 100% Binder   3.5   3.5 Carbon Powder  3.5 2 50% Carbon/50% Binder 2 1 1st Step: 100% Binder 1 1 2nd Step:95% Carbon/5% Binder

[0015] Odor Rating: (no odor) 1 . . . 5 (strong odor) One drop of onionjuice per jar. LDPE substrate.

[0016] The test samples contained equivalent amounts of activatedcarbon. For example, almost twice the surface area of the 50/50carbon/binder coating was used compared with the 95/5 sample preparedwith two steps. The results indicate that the 50/50 coating wassubstantially as effective at negating the onion odor after 24 hours asthe 95/5 sample, however the latter coating with a greater concentrationof activated carbon at the film surface was more effective after 1 hour.

[0017] Accordingly it will be seen that the novelty of the presentinvention lies in the technique for applying the greatest concentrationof carbon available at the film surface with little or no rub off. Theamount of carbon necessary to accomplish the desired odor abatementresult will depend in the first instance upon the strength of the odordesired to be eliminated or absorbed. For the purposes of the presentinvention, an effective application of activated carbon is intended tomean sufficient carbon to absorb substantially all of the odor presentin the packaged product or waste. Since the total amount of carbonrequired for any specific application cannot be defined with anyspecificity, a trial and error process may be involved.

[0018] While only a preferred embodiment of the present invention hasbeen fully described, it will be obvious to those skilled in the artthat various modifications and substitutions could be made in theinvention without departing from the scope of the invention as definedin the appended claims.

What is claimed is:
 1. A method for making a substantially flexible odorabsorbing packaging material comprising: (a) selecting a flexiblesubstrate; (b) preparing a first odor sorbing coating compositionconsisting essentially of activated carbon and binder wherein saidbinder is capable of wetting out the surface of the substrate of step(a); (c) applying the first odor sorbing coating to the substrate ofstep (a); (d) drying the coating of step (c); (e) preparing a secondodor sorbing coating composition consisting essentially of activatedcarbon and binder wherein the concentration of activated carbon in thesecond coating is greater than the activated carbon concentration of thefirst coating; (f) applying the second odor sorbing coating to thesubstrate over the dried residue of the first coating; and, (g) dryingthe substrate.
 2. The method of claim 1 wherein the flexible substrateis a polymeric film selected from the group consisting of poly-olefins,polyesters, and polyamides.
 3. The method of claim 2 wherein the bindercomponent of the two coating compositions of steps (b) and (e) comprisesan aqueous emulsion selected from the group consisting of styrenes,acetates, and urethanes.
 4. The method of claim 3 wherein the carboncontent in the first coating composition comprises 0-50% by weightactivated carbon.
 5. The method of claim 4 wherein the carbon content inthe second coating composition comprises 50-95% by weight activatedcarbon.
 6. The method of claim 5 wherein the activated carbon has aparticle size within the range 5-40 microns.
 7. The method of claim 6wherein the flexible substrate is low density polyethylene.
 8. Themethod of claim 7 wherein the binder is an aqueous emulsion of styreneacrylate.
 9. Odor absorbing packaging material comprising asubstantially flexible substrate having applied to at least one surfacethereof an odor sorbing coating wherein said coating comprises fromabout 50-95% by weight activated carbon and from about 5-50% by weightbinder.
 10. The packaging material of claim 9 wherein said substratecomprises a polymeric film selected from the group consisting ofpolyolefins, polyesters and polyamides.
 11. The packaging material ofclaim 10 wherein said binder comprises an aqueous emulsion selected fromthe group consisting of styrenes, acetates, and urethanes.
 12. Thepackaging material of claim 11 wherein the substrate is low densitypolyethylene and the binder is an aqueous emulsion of styrene acrylate.